If you honestly feel that you are in any kind of danger, you need to speak with an attorney right away. That being said, it doesn't sound as if you have any current litigation with your new wife. The purpose of a subpoena, generally, is to force a witness to appear before some kind of court or other tribunal and give testimony or produce documents. Another avenue is to potentially contact your phone company and see if they have any way of giving you the texts. But for a subpoena, you're most likely going to need an attorney. Good luck to you!